Electric coupling system



June 10, 1930. c, E, TRUBE 1,762,431

ELECTRIC COUPLING SYSTEM Filed Jan. 9. 1924 23 27 I, ZZ 4 OUTPUT l l v I INVENTOR CarZE Pubs ATTORN EY Patented June 10, 1930 UNITED STATES PATENT OFFICE CARL E. TRUBE, OF MAPLEWOOD, JERSEY, ASSIGNOR TO HAZELTINE CORPORA- TION, 0F JERSEY CITY, JERSEY, A CORPORATION OF DELAWARE ELECTRIC COUPLING SYSTEM Application filed January 2 1824, Serial No. 685,148, and in Mexico January 22, 1925. i

This invention relates to electric coupling systems, more particularly for the amplification of electrical impulses having a relatively hi h frequency. I

n the amplification of electrical impulses it has been found difficult to obtain satisfactory amplification because of capacitative effects between elements of the apparatus employed. Such capacitative effects make possible undesired local oscillations, the tendency to the generation of which materially reacts upon the degree of effectiveness of the amplifier.

It is an object of the present invention to make available for subsequent use over a relatively wide range of frequencies the energy caused to flow in the output circuit of an I amplifier at the same time governing the tendency to make the amplifier act in itself as a generator of local oscillations.

The invention has perhaps its widest field of utility'in connection with an amplifier of the vacuum tube type as a means of coupling between adjacent vacuum tubes arranged in so called cascade relationship,'or. as a means of coupling between any types of apparatus depending for their operation on a supply of electrical impulses wherever the tendency to generate local. oscillations as a result of capacitative feedback on the part of any portion ofthe apparatus is detrimental to the operation of the system. It may, however, be employed in connection with amplifiers of any desired type having the capacitative characteristics above referred to.

Other objects and features of the invention will appear from the following description taken in connection with the appende claims. I j

Vacuum tube as used in this application refers to any thermionic device comprising an input electrode referred to as the grid, an output electrode, referred to as the plate and a common electrode, referred to as the filament; the electric power output being controlled by the input voltage between the grid and the filament.

Electric coupling system as 'used in this application refers to any electric circuit arrangement interposed between a vacuum tube and some succeeding device which circuit is arranged to utilize power released by the vacuum tube for the building up of a reso-, nant voltage for impression on the input terminals of the succeeding device.

By input impedance as referred to in this application is meant the impedance of the electric coupling system or circuit arrangement between the filament system and in the plate circuit of a vacuum tube, the

variations in voltage between the elements within the tube may readil be made such that energy will be fed back rom the plate to the grid circuits through the plate-grid capacity of the tube. Such feedback will tend to cause the tube to act as a generator of local oscillations which will interfere with the proper operation of the vacuum tube as an amplifier. To prevent such oscillations, it has been customary to introduce opposing reactions, such as sources of loss or couplings between the plate and grid circuits whichwill oppose that of the plategrid capacity. Sources of loss have the disadvantage of lowering the selectivity in a tuned amplifier;

and opposing couplings introduce complications of construct-ion and adjustment that may increase the cost. In accordance With this invention the effectiveness of the capacitative feedback is so reduced by limiting the alternating component of voltage between the plate and the filament that oscillations are prevented without introducing any opposing reactions; or, in other words, the

operation of the amplifier is madestable.

essentially by employing a sulficiently lpivm input impedance in the coupling system.

the same time, a satisfactory degree of amplification, together with high selectivity, is secured bybuilding up between the output te inals of the coupling system a resonant 5 vo tag many times higher than the filamentplate voltage. 1 r

A feature of this invention is the prov1s1on of means for maintaining the conditions just stated over a relatively wide range in frequency, by suitably varying the ratio of the resonant output voltage to the filament-plate Volta e.

Re erring to the drawings a Fig. 1 shows diagrammatically one form of the invention embodied in a stage of a tuned radio-frequency amplifier, in which the amplitude of -filament-plate voltage variation is limited.

Fig. 2 shows diagrammatically a modified form of the invention including an insulating transformer in the electric coupling system.

Referring to Fig. 1, there is provided a three-electrode vacuum tube-10 of the amplifying type, which may comprise an evacuated chamber 11 formed of glass or the like. The

vacuum tube 10 includes a heated filament 12 for emitting electrons, a plate 13 upon which the electrons impinge and a grid 14 forcontrolling the passage of electrons. For heating the filament 12, a source-0f energy, such as abattery 15, is provided, the filament current being controlled by means of a usual filament rheostat 16.

For maintaining the plate 13 at a high positive potential relative to the filament 12, there is provided a source of electric potential, such as a battery 20, having its negative terminal connected to one terminal of the filament. Included in the circuit-of the battery- 20 is a choke coil 21 preferably so constructed as to have a minimum capacity be tween its windings. There is also provided a pair of condensers 22, 23 and an inductance 24 connected in series with a conductor 25 and a conductor 26, collectively forming a closedv oscillatory circuit 22, 25, 23, 24, 26, 20, which may be tuned to resonance with any desired preselected frequency. In case it is not desired to include the plate battery 20 in the oscillatory circuit, it may be connected immediately adjacent the filament battery 15, as is the more common practice. The position of the plate battery has no particular relation to this invention. The terminals of the inductance 24 are connected to binding posts 27,28 respectively, which form the output terminals of the amplifier stage and which may be connected to a subsequent stage, to a' detector or to any other desired device. The capacities of condensers- 22 and 23 are so arranged as to be varied simultaneously, as for example by means of a single manual device, such as a knob, whereby the 6.5 frequency adjustment of the system is made.

The ratio of capacities of condensers 22 and 23 for effective operation at each setting, 1s determined by the constants of the vacuum tube 11 and of the coil 24. For the amplifi cation of electrical impulses having frequencies ranging from 500,000 to 1,500,000 cycles per second, the capacity of the condenser 22 may be, for example, eight to fifteen times that of condenser 23, when using a coil of ordinary size and an ordinary radio receiving vacuum tube having a mutual conductance of 0.3 to 0.4 millimho; with vacuum tubes of higher mutual conductance, ;the ratio of capacities should be correspondingly higher. The ratio of capacities of the conclensers may be preselected for any desired rangeof adjustment.

The grid 14 of the tube 10 is connected to an input terminal 30 by means of a conductor 31 and one of the terminals of the filament 12 is connected to an input terminal 32 by means of a conductor 33. Thus when a voltage is applied across the terminals 30, 32, there is produced a voltage between the grid 14 and the terminal of the filament 12. The action of thevacuum tube in a well known manner, as a result of this voltage, produces a change in the plate current flowing between the plate 13 and the filament 12 and thus a change in the current in the external plate circuit. The -choke coil 21 effectively resists changes in current passing therethrough. Accordingly, a change in the plate current must produce a change in the electrostatic charge of the condenser '22, and this condenser gives out or receives energy in proportion to the change in plate-filament conductance. tively large, governs the variations in filament-plate voltage. The change of voltage across the terminals of the condenser 22 upsets the equilibrium existing in the resonant circuit 22, 25, 23, 24, 26, 20 wherein the alternating voltage across the joint capacity 22, 23 is equal and opposite to that across the inductance 24. It follows that the voltage across 23, 24 changes in accordance with the voltage across the condenser 22 and that the .a resonant circuit in which a relatively high resonant voltage is built up.

Referring now to Fig. 2, there is provided a vacuum tube 10 and associated therewith a filament heating battery 15 and "a plate potential battery 20, as in Fig. 1. In this modi- Hence the condenser 22 if relafiedform of the invention which materially difi'ers from the form of Fig. 1 only in that the main resonant circuit is insulated from ductor 305. 'The other terminal of the primary winding 303 is connected in series with a choke coil 306 to. the positive terminal of the battery 20.

For by-passing variations in plate current t ere is provide-d in shunt collectively with the battery 20 and the choke coil 306, a condenser 310. In shunt with the secondary winding 304 of the transformer 302 is a variable condenser 311 which in combination with the winding 304 forms a closed oscillatory circuit 312 which may be tuned to the frequency of the actuatingimpulses. The circuit 312 is connected to the terminals 313, 314 by means of conductors 315, 316 respectively. The condenser 301 of Fig. 2 corresponds to condenser 22 of Fig. 1, and the coil 306 correspondsto coil 21 of Fig. 1. The capacities of the condensers 301 and 310, are preferably selected so that the capacity of the condenser 301 is much greater than that of the condenser 310 and so that their joint capacity in shunt with the coil 303 will not cause the circuit including capacities 301, 310 and the coil 303 to be resonant to any frequency at whichthe device is to be operated.

With this arrangement it is advantageous to arrange condensers 310 and 301 so that the ratio of the magnitudes of their capacities can be altered at will, in order to obtain the best operating condition at any frequency to which the system may be tuned. Since the magnitudesof the capacities 310, 301 and 311 are interdependent for best effectiveness and since the combination of condensers 310 and 301 in connection with the inductance of coil 303 is preferably so chosen as not to greatly alter the tuning of .circuit 312, either of condensers 310 and 301 may be made of fixed capacity, and the desired Ihange in ratio of their capacities secured by making the other of the two of variable capacity.

In operation, the condenser 301 may be assumed to determine the amplitude of filament-plate voltage Variation. At the same time condenser 301 determines the voltages set up in coil 303 and condenser 310 as a result of energy flow to maintain proper voltage distribution in circuit 301, 303, 310. Such flow of current through coil 303 will produce variations in flux associated with coil 303, causing the building up of a resonant voltage in the coupled oscillatory circuit 312. This resonant voltage may be made considerably the largest of any generated in the output circuit, and may be arranged for subsequentnseby connections to output terminals as shown.

It will be seen that by application of the principle of governing the variations in filament-plate potential difference, I have made it possible to amplify impulses ofhigh frequencies without objectionable inter-element capacitative transfer of energy from the plate to the grid circuits of the vacuum tube, thus mitigating the undesirable tendency of the vacuum tube to act in itself as a generator of local oscillations. The amplifier may, therefore, be operated with a high degree of eiiectiveness.

Although certain specific embodiments of the invention have been particularly shown and described, it will be understood that the invention is capable of modification and that changes in the construction and in the arrangement of the various cooperating parts may be made without departing from the spirit or scope of the invention, as expressed in the following claims.

WVhat I claim is:

1. In a vacuum tube coupling system, the combination of a condenser connected directly from the plate to the filament system of a vacuum tube whereby the amplitude of the alternating voltage between the plate and the filament system is limited, independent means for completing a path for the direct plate current of said tube, a second condenser having one of its terminals connected to one of the terminals of the plate-filament condenser, a winding connected to the other terminal of thesecond condenser and to the side of the plate-filament condenser which is not connected to said second condenser, said winding forming with said condensers a closed resonant circuit in which the condensers are in series, andmeans for rendering a resonant voltage obtained from said winding available for subsequent use.

2. In a vacuum tube coupling system, the combination of a condenser connected directly from the plate to the filament system of a vacuum tube whereby the amplitude of the alternating voltage between the plate and the filament system is limited, independent means for completing a path for the direct plate current of said tube, a second condenser having one of its terminals connected to one of the terminals of the plate-filament condenser, a winding connected to the other terminal of the second condenser and to the side of the plate-filament condenser which is not connected to said second condenser, said winding forming with said condensers an adjustable closed resonant circuit in which said condensers are in series, said resonant circuit comprising three units, at least one of which units is adjustable, and means for rendering a resonant voltage obtained from said winding available for subsequent use.

3. In a radio-receiving amplifier stage the Combination of a vacuum tube having a filament, a grid and a plate, anelectric coupling system including self-inductance and capacity, output terminals insaid coupling system between which a resonant voltage is built connections from sa1d filament and said u plate to said coupling system, said coupling system including adjustable tuning'fmeans and capacitative means simultaneously adjustable with said tuning means for maintaining at all frequencies the 1111310 I resonant voltage to the voltage between said filament and said plate at such value as tb maintain highly effective amplification and stable operation of said stage.

4. In a radio-receiving amplifier stage the to tune said coupling system and to maintain throughout the tuning range such ratio of said resonant voltage to the voltage between said filament and said'plate as to maintain highly effective amplification and stable operation of saidstage.

5. A radio-frequency amplification system associated with the plate circuit of a vacuum tube having afilament, a grid and a' plate, said system including a condenser connected between the plate and the filament of said tube, and a second condenser and an inductance coil effectively connected in series with each other and between said plate and said filament, said second condenser having a smaller capacity, whereby the alternating voltage between said plate and said filament is much less than that across said coil and is in said oscillatory circuit between which the insuflicient to cause local oscillations.

6. A radio-frequency amplification system associated with the plate circuit of a vacuum tube having a filament, a grid and a plate, said system including a condenser connected between the plate and the filament of said tube, and a second condenser and an inductance coil effectively connected in series with each other and between said plate and said filament, said second condenser having a smaller capacity, whereby the alternating voltage between said plate and said filament is much less than that across said coil and 1's lnsuificlent to cause local-osc1llat1ons,"said two condensers belng controlled simultaneously by a singlemanual means, whereby the of said associated with the plate circuit of a vacuum tube having a filament, a grid and a plate,

said system including a condenser connected between the plate and the filament of sald tube, and a second condenser and an inductance coil effectively connected in series with each other and between said plate and said -filament, said second condenser having a smaller capacity, whereby the alternating Voltage between said plate and said filament is much less than that across said coil and is insufficient to cause local oscillations, said two condensers being adjustable simultaneously by a single manual control, whereby the ratio of their capacities is maintained at a desired value while the resonant frequency of the circuit in which said condensers are connected is varied throughout a required frequency band by said manual control.

.8. In a radio receiving amplifier stage, the combination of Vacuum tube having a filament, a grid, and a plate, an electric coupling system including self-inductance and a plurality of capacities forming at least one closed oscillatory circuit, output terminals in said coupling system between which a resonant voltage is built up, connections from said filament and said plate to points in said oscillatory circuit between which the alternating voltage accompanying said resonant Voltageis maintained so low by means of a ratio between the values of said capacities that highly selective amplification and stable operation are secured. i a

9. In a radio receiving amplifier stage, the combination of a vacuum tube having a filament, a grid and a plate, an electric coupling system including at least one closed oscillaalternating voltage" accompanying said resonant voltage 1s maintained so low by means of a who between the values of said capacstory circuit having therein self-inductance ities that highly selective amplification and stable operation are secured.

In witness whereof, I have hereunto set my hand this 4th day of January, 1924.

' CARL E. TRUBE.

ratio of their capacities is maintained at a.

desired value while the resonant frequency of the circuit in which said condensers are connected is varied over the required. frequency range.

' 7. A radio-frequency amplification system 

